微载荷含油轴承摩擦性能研究 Ⅱ.摩擦试验分析

采用自行研制的径向轴承微载荷摩擦试验机研究了微载荷下径向含油轴承的摩擦性能，采用小波方法对试验数据进行滤波降噪．结果表明，含油轴承在稳定微载荷状态下的瞬态摩擦系数不固定，且随着润滑剂、轴承转速、径向载荷与混合润滑状态等因素而变化．在微载荷状态下，当600r／min、采用液晶添加剂（5CB）与46号机械油以体积比1％-2％配制的润滑剂润滑时，平均摩擦系数达到最小值；当转速从600r／min增至3000r／min时，平均摩擦系数由小变大、再变小；瞬态摩擦系数随着载荷从0．5N增至10．0N呈现高-低-稳定的变化趋势．与混合润滑状态相比，充分润滑下的摩擦系数较大；当混合润滑时，在主轴转速为1500—2400r／min下的摩擦系数出现不稳定．

微载荷含油轴承摩擦性能研究 Ⅰ.摩擦试验机设计

研制了1种针对径向轴承的微载荷摩擦试验机,介绍了其工作原理及结构,即利用外加载荷抵消浮动测试架重量以施加微小载荷,并利用激光位置传感器(PSD传感器)实现无接触位移测量;同时测量了摩擦副的转动角度并计算出摩擦系数;采用摩擦转角测量法和外加力矩平衡摩擦法测量微载荷下的摩擦性能,以测量时间末端位置作为位置基准,通过极限偏载平衡进行载荷标定.结果表明:微载荷摩擦试验机可应用于径向轴承在微小载荷下的摩擦力测量;可以通过在较大范围内设置结构参数来研究径向轴承的摩擦特性;并可利用数据采集技术研究速度和载荷连续变化条件下的摩擦性能.

国外微纳遥感载荷技术最新进展

随着技术的进步和商业应用模式的创新,微纳遥感卫星和载荷的发展得到了各领域的重点关注。相比传统遥感载荷,微纳遥感载荷体积小、质量小、研制周期短、成本低、发射方式灵活,很好的适应了商业航天发展,满足多种行业应用。目前,国际上多家企业和研究机构推出了各种高性能微纳遥感卫星计划,配备的载荷各有特点。文章对国际典型微纳遥感载荷进行了调研分析,可以看出目前国际微纳遥感载荷通常会采用新技术以提升性能,采用标准化、型谱化研制理念提高研制效率,并且星上智能处理技术也愈发被重视,以期减小卫星数传压力。文章根据国际微纳遥感载荷发展特点并结合中国航天自身情况,形成了启示与建议,为中国微纳遥感载荷未来发展提供参考。

Mg-Mn-Ce镁合金表面功能纳米有机薄膜的制备与摩擦学特性

通过有机镀膜技术在Mg-Mn-Ce镁合金表面制备了有机薄膜,采用接触角测量仪测定了有机薄膜的蒸馏水接触角,使用椭圆偏振光谱仪测试了薄膜厚度,利用X射线光电子能谱仪(XPS)表征了薄膜表面典型元素的化学状态,使用原子力显微镜(AFM)观察了薄膜的表面形貌,并借助于纳米划痕测试仪评价了薄膜在微载荷下的摩擦学特性.研究结果表明:有机镀膜后镁合金表面形成了有序的纳米有机薄膜,有机薄膜与蒸馏水的接触角数值为108.6°(未处理镁合金基体与水的接触角为45.8°),实现了由亲水向疏水功能特性的转变;未处理镁合金基体的摩擦系数为0.127,有机镀膜后镁合金的摩擦系数为0.078,因此疏水性纳米薄膜能够有效降低摩擦系数.

Damage of concrete attacked by sulfate and sustained loading

The damage processes of ordinary concrete and high strength concrete, attacked by solutions of 2. 5%, 5. 0% and 10% Na2SO4（mass fraction）are studied. And the effects of flexural loads with stress ratios of 25% and 50% of the initial flexural strength on the damage process of concrete are also investigated. The results show that the damage process of concrete attacked by sulfate salt exhibits an initial damaged stage, a performance improving stage and a performance worsening stage. When the concentration of Na2SO4 in a solution increases from 2. 5% to 5.0%, the service time of the concrete decreases approximately 25%. Furthermore, it decreases to even 40% with an increase in a Na2SO4 concentration up to 10%. And the flexural load accelerates the deterioration rate of the concrete in the latter period. The stress ratio increases from 0 to 25%, the failure time of the concrete decreases 15% ; and the failure time decreases between 25% and 35% when the stress ratio increases from 25% to 50%. In addition, sulfate corrosion products of concrete are studied by SEM （scanning electron microscopy）, EDS （energy disperse spectroscopy） and XRD（X-ray diffraction）.

Degradation mechanism of rock under impact loadings by integrated investigation on crack and damage development

Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.

Effect of microvoids on microplasticity behavior of dual-phase titanium alloy under high cyclic loading(Ⅰ):Crystal plasticity analysis

A crystal plasticity finite element(CPFE)model was established and 2D simulations were carried out to study the relationship between microvoids and the microplasticity deformation behavior of the dual-phase titanium alloy under high cyclic loading.Results show that geometrically necessary dislocations(GND)tend to accumulate around the microvoids,leading to an increment of average GND density.The influence of curvature in the tip plastic zone(TPZ)on GND density is greater than that of the size of the microvoid.As the curvature in TPZ and the size of the microvoid increase,the cumulative shear strain(CSS)in the primaryα,secondaryα,andβphases increases.Shear deformation in the prismatic slip system is dominant in the primaryαphase.As the distance between the microvoids increases,the interactive influence of the microvoids on the cumulative shear strain decreases.

Microstructure and Mechanical Properties of Ti-4Al-1.5Mn Resistance Spot Welding Joints

Ti-4Al-1.5Mn dual phase titanium alloy sheet was spot welded by pneumatic resistance spot welder.The effects of different welding parameters on shear load and nugget diameter were studied.The results show that the maximum shear load of solder joint increases first and then decreases with the increase of electrode pressure and welding current,while the nugget diameter increases with the increase of electrode pressure and welding current.Electrode pressure of 0.20 MPa and welding current of 46 A are the optimal process parameters,under which the maximum shear load of solder joint reaches 8.80 kN.The microstructure of nugget zone is coarse acicular martensite,and the solder joints fail in a mixed mode of intergranular brittle-ductile fracture.

Time Domain Calculation of Connector Loads of a Very Large Floating Structure

Loads generated after an air crash, ship collision, and other accidents may destroy very large floating structures （VLFSs） and create additional connector loads. In this study, the combined effects of ship collision and wave loads are considered to establish motion differential equations for a multi-body VLFS. A time domain calculation method is proposed to calculate the connector load of the VLFS in waves. The Longuet-Higgins model is employed to simulate the stochastic wave load. Fluid force and hydrodynamic coefficient are obtained with DNV Sesam software. The motion differential equation is calculated by applying the time domain method when the frequency domain hydrodynamic coefficient is converted into the memory function of the motion differential equation of the time domain. As a result of the combined action of wave and impact loads, high-frequency oscillation is observed in the time history curve of the connector load. At wave directions of 0° and 75°, the regularities of the time history curves of the connector loads in different directions are similar and the connector loads of C1 and C2 in the X direction are the largest. The oscillation load is observed in the connector in the Y direction at a wave direction of 75° and not at 0° This paper presents a time domain calculation method of connector load to provide a certain reference function for the future development of Chinese VLFS

Axial bearing behavior of super-long piles in deep soft clay over stiff layers

In order to find out the bearing behavior of super-long piles located in deep soft clay over stiff layers around Dongting Lake, China, a test pile was first designed with the field loading test finished afterward. Based on the measured test results, load transfer mechanism and bearing behavior of the pile shaft were discussed in detail. Then, by introducing a bi-linear model for shaft friction and the tri-linear model for pile tip resistance, respectively, the governing differential equation of pile soil system was set up by the load transfer method with the analytical solutions derived as well, taking into account the effect by stratified feature and various bearing conditions of subsoil, material nonlinearity, and the sediment under pile tip. Furthermore, formulas to determine the axial capacity of super-long piles by the pile top settlement were advised and applied to analyze the test pile. Good agreement between the predicted load settlement variations and the measured data is obtained to verify the validity of the present method. The results also show that, the axial bearing capacity of super-long piles should be controlled by the allowable pile top settlement, and buckling stability of the pile shaft should be paid attention as well.

Wavelet time series MPARIMA modeling for power system short term load forecasting

The wavelet power system short term load forecasting(STLF) uses a mulriple periodical autoregressive integrated moving average(MPARIMA) model to model the mulriple near periodicity, nonstationarity and nonlinearity existed in power system short term quarter hour load time series, and can therefore accurately forecast the quarter hour loads of weekdays and weekends, and provide more accurate results than the conventional techniques, such as artificial neural networks and autoregressive moving average(ARMA) models test results. Obtained with a power system networks in a city in Northeastern part of China confirm the validity of the approach proposed.

Experimental and Analytical Study of Torsional Vibration under Multiaxial Loading in Time Domain

The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations need coefficients and parameters that, usually, must be experimentally estimated. This work uses a resistive electric SG （strain gage） to dynamically determine strains produced in the shaft due to harmonic oscillatory motion under multiaxial loading. This movement is simulated on a prototype specially developed for this purpose. It comprises a pulley attached to the end of a stepped cantilevered shaft, which is clamped at the opposite end. In this configuration, a cam generates a torque to the system, springs regulate the stiffness and the damping coefficient of the assembly, as well as they can be suitably adjusted to produce an underdamped condition. The main advantage, highlighted in this study, refers to a major simplification. Although the system under study shows multiple degrees of freedom （torsion and bending）, the shape and the positioning of linking SGs with the resistor bridge （Wheatstone Bridge）, allow ＂to evaluate the loading effects independently, as if only one degree of freedom of the system exists at a time domain. Strains graphs for two forms of cyclic torsional oscillation, analytical and experimental, were successfully generated.

Ultimate bearing capacity of concrete dam involved in geometric and material nonlinearity

To get the actual ultimate bearing capacity of concrete dam, the effect of geometric nonlinearity and strain softening on it, which appears in the failure process of concrete dam, is studied. Overload method is adopted to obtain the bearing capacity of a concrete dam by taking into consideration strain softening in the material constitutive law, geometric nonlinearity in geometric equation and equilibrium differential equation. Arc-length method is used to find the extreme point and descending branch of the load-displacement curve of the dam. The results present that the effect cannot be ignored. And geometric nonlinearity of structure and strain softening of materials should be considered for numerical analysis of ultimate bearing capacity of a concrete dam.

Flexural response of doubly curved laminated composite shells

In the present work, analytical solutions for laminated composite doubly curved panels on rectangular plan form undergoing small deformations and subjected to uniformly distributed transverse load have been obtained. The problem is formulated using first order shear deformation theory. The spatial descretization of the linear differential equations is carried out using fast converging finite double Chebyshev series. The effect of panel thickness, curvature, boundary conditions, lamination scheme as well as material property on the static response of panel has been investigated in detail.